From 1980-1991 82 (7.2%) of 1134 tuberculosis notifications in Edinburgh were for pleural effusion. Study of the available records of 62 cases satisfying defined diagnostic criteria identified 14 cases (6 M, 8 F) with a mean age of 27.6 years (range 11-51 years) of primary tuberculous effusion and 25 cases (21 M, 4 F) with a mean age of 51 years (range 19-79 years) with pleural effusion due to reactivation disease. Twenty-three patients (19 M, 4 F) with a mean age of 48.9 years (range 25-85 years) defied classification. Symptoms, associated and diagnostic test findings were similar in all three groups of patients. Parenchymal radiographic shadowing was seen in 1/14 primary, 16/25 reactivation and 3/25 unclassified pleural effusions. Twenty-three of 30 patients treated with corticosteroids showed no residual radiographic abnormality compared to 17/30 not so treated (P < 0.06). Reactivation disease is currently a commoner cause of tuberculous pleural effusion than primary disease in Edinburgh. We suggest that the unclassified cases, so similar in age and sex to the defined reactivation disease cases, also represent largely extrapulmonary reactivation disease occurring in middle age.